The invention relates to a three-dimensional design of a measuring module with an optoelectronic assembly and a scanning plate.
European Patent Application 838 665 A1 describes an optical length-measuring device that is composed of a scale, a light source, and a scanning assembly having a scanning grating. The light source transmits collimated light to the scale, which supports an optical graduation. The scanning assembly detects fluctuations in brightness according to the displacement between the scale and the scanning assembly. The scanning assembly has thin-film conductors, on a glass substrate, and a light-sensitive optical chip which includes a group of light-sensitive components and the scanning grating. The scanning assembly is arranged on the other side of the scale, so that the light-sensitive optical chip receives the collimated light. The lightsensitive optical chip is mechanically secured by soldering and by an underfiller, a transparent seal that is applied between the optical chip and the glass substrate.
One disadvantageous aspect of this system is that the circuits applied to the glass substrate of the scanning assembly require a large surface, as a result of which relatively long printed circuit traces are required, in particular for connecting to a signal processing unit.
European Patent Application 564 683 A1 describes an optoelectronic position-, angle-, or rotation measuring device. The device has an illuminated or transparent code carrier having at least one code track. Next to the code track, a diaphragm is arranged in the form of a plate having a transparent area assigned to the code track. In addition, an optoelectronic sensor is arranged on the side of the diaphragm facing away from the code carrier, the sensor having a sensor surface facing the diaphragm. On the plate-shaped diaphragm there is an optoelectronic semiconductor chip used as a sensor, disposed on the side facing away from the code carrier. The chip has contact points on the side facing the plate-shaped diaphragm. The plate has electrical printed circuit traces corresponding to these contact points, the printed circuit traces being connected in an electrically conductive manner to the contact points of the semiconductor chip via soldering points. Using a molding compound, for example, the semiconductor chip can be also stabilized mechanically.
This system also has the disadvantage that the sensor, including the necessary evaluation electronics, requires a relatively large amount of space, and therefore long printed circuit traces are necessary.
German Patent Application 197 20 300 A1 discloses an electronic hybrid component and a method for manufacturing it. In this component, at least one cavity is introduced, using a chip-on-chip arrangement, in a substrate that constitutes the first chip. An electrical insulating layer, having a metal layer arranged on top of it, is applied to the cavity. A second chip arranged in the cavity in the form of a light-emitting diode is conductively connected to the metal layer and extends out of the cavity, beyond the first chip, by at most a very small amount. The cavities in the first chip are generated using anisotropic etching. The insulation is obtained through oxidation of the surface of the first chip or through the deposition of an insulating layer. The metallization can contain a multiple metallization system and can be patterned using a photolithographic process. The second chip, arranged in the cavity, contacts the metallization thus generated in the cavity and is also brought into contact with the first chip on the reverse side.
This hybrid component has the disadvantage that the cavity and its layers, as well as the contacting between the two chips, can only be made in a relatively complicated fashion. Furthermore, it is not described in the reference how it would be possible, using a chip-on-chip arrangement, to optimize a measuring module so as to make a compact length- or angle-measuring system.
The article xe2x80x9cNew Dimensions in Position and Angle Measuring Technology,xe2x80x9d by Reiner Burgschat, in F and M Feinwerktechnik, Mikrotechnik, Mikroelektronik (Precision Engineering, Microtechnology, Microelectronics), October 1996, p. 752-756, describes a measuring module formed in a single-plane circuit on a glass substrate. The light-emitting diodes necessary for a measuring system are applied and contacted on the surface of an optical chip such that they emit a beam through the glass substrate. The optical chip has a photo diode array that is soldered onto the glass substrate using flip-chip technology, and that detects the beam passing through the glass substrate. To connect the individual components, a printed circuit trace pattern is applied on the glass substrate connecting the optical chip components to the electronic signal conditioning. In addition, the glass substrate also has a scanning graduation. An underfiller is applied between the optical chip having the photo diode array and both the light-emitting diodes and the glass substrate to improve mechanical stability. To protect this measuring module, a ceramic cap is secured over the assemblies applied to the glass substrate.
A disadvantageous feature of this system is that the entire circuit is formed in one plane, which makes a relatively large glass substrate necessary and results in long printed circuit traces on the glass substrate. The sensitivity to interfering emissions is increased, and the electrical resistance of the traces is high. Furthermore, the underfiller can reach the beam path between the light-emitting diode, the scanning grating, the scale, and the photo diode array, detracting from the optical properties of the arrangement.
European Patent Application 060 021 A2 describes arranging an optoelectronic assembly on a printed circuit board over a scanning pattern of a rotary transducer. On the other side of the printed circuit board, additional assemblies are arranged for signal processing.
A disadvantage of this system is that the assemblies are separated by a printed circuit board, which necessarily results in a relatively large overall height of the optoelectronic assemblies, printed circuit board, and signal processing unit, which are arranged in three-dimensional fashion one over the other.
European Patent Application 789 228 A2 describes how to arrange printed circuit traces on a transparent substrate, creating a connection between a printed circuit board and an optoelectronic assembly. The connecting points between the printed circuit traces of the printed circuit board, the transparent substrate, and the optoelectronic assembly are also used for mechanically fixing in position the transparent substrate and the optoelectronic assembly.
This device has the disadvantage that the arrangement achieves only slight mechanical stability. Although it is necessary to achieve the most exact possible orientation of the optoelectronic assembly with respect to the transparent substrate and the printed circuit board, a change in the arrangement, such as the separation of a printed circuit trace, can be caused even by minor mechanical shocks.
The present invention is thus a circuit arrangement for a measuring module, composed of an optical unit and signal processing electronics, that can be assembled in a very small design, so that the lengths of the electrical printed circuit traces are as short as possible, in particular between the optical sensor and the evaluation electronics. In addition, the necessity for mechanical stabilization through the use of an underfiller is substantially eliminated in this design.
In one embodiment, the invention is a three-dimensional measuring module, that includes a scanning plate, an optoelectronic assembly disposed over the scanning plate, a signal processing unit disposed over the optoelectronic assembly, and a protective cap cooperating with the scanning plate to substantially enclose the optoelectronic assembly and the signal processing unit.
The method according to the invention has the advantage that due to the three-dimensional arrangement of optical unit and signal processing electronics, located one over the other, the connecting printed circuit traces can be kept very short. In this manner, the electrical resistances of the printed circuit traces are small, so that even a weak output signal of the optical sensor can still be recognized without error by the signal processing electronics. Furthermore, another advantage is that the sensitivity to interfering emissions, which above all are received through long printed circuit traces which act as antennas for the interfering emissions, is significantly less due to the fact that the printed circuit traces between the optical sensor and the signal processing electronics are very short.